Without limiting the scope of the present invention, its background is described with reference to a downhole control system operating in a wellbore that traverses a hydrocarbon bearing subterranean formation, as an example.
It is well known in the subterranean well production art that production of hydrocarbon fluids can be improved by installing well monitoring equipment and completion components that can be adjusted during the life of the well. For example, certain well installations may include some combination of zonal isolation devices, interval control devices, downhole control systems, permanent monitoring systems, surface control and monitoring systems, distributed temperature sensing systems, data acquisition and management software and system accessories.
Once production begins, data from the well monitoring equipment can be used, for example, to regulate downhole flow control devices to control production from the various zones. Using a plurality of flow control devices allows an operator to selectively receive or restrict production from the different zones by opening, closing or choking flow through specific flow control devices. Typically, the actuation of such flow control devices may be accomplished with a hydraulic control system. In one implementation, each flow control device has two control lines associated therewith, one acting on either side of the actuation piston to open, close and partially close the flow control device. In this implementation, if there are three flow control devices in the completion, six control lines are required. In a more recent implementation, a common control line is associated with one port of each of the flow control devices with individual controls lines being run to the other port of each of the flow control devices. This implementation is known as an N+1 control system wherein N is the number individual control lines that run to the flow control devices and the plus 1 refers to the common control line. In this implementation, if there are three flow control devices in the completion, four control lines are required.
Regardless of the exact hydraulic control system implementation, it has been found that there is often a limitation on the number of control line penetrations that can be made, for example, at the wellhead, the tubing hanger, the production packer or through other well equipment. As such, the number of flow control devices or other hydraulically controlled devices in a completion is limited to no more than half the number of control line penetrations in a two control line implementation. Similarly, the number of flow control devices or other hydraulically controlled devices in a completion is limited to no more than one less than the number of control line penetrations in an N+1 implementation.
A need has therefore arisen for an improved downhole control system for actuating hydraulically controlled devices positioned in a well that enables control over a greater number of hydraulically controlled devices with a limited number of control lines.